1. Field of the Invention
The present invention relates to a coating treatment apparatus, a coating treatment method, and a non-transitory computer storage medium, for supplying a coating solution to a substrate to form a coating film.
2. Description of the Related Art
In a photolithography process that is one of semiconductor manufacturing processes includes a process of applying a resist onto the front surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) to form a resist film. The formation of the resist film is performing by a so-called spin coating of discharging a resist solution from a nozzle onto a central portion of the wafer rotated at a high speed and spreading the resist solution to the peripheral portion by the centrifugal force.
It is discussed to reduce the use of the expensive resist solution and form the resist film with a small amount of resist solution. When using a small amount of resist solution as described above, the resist film to be formed is more likely to be affected by the discharge state of the resist solution, so that even if the discharge state of the resist solution is slightly varied, a coating mottle different in thickness from the surroundings is possibly formed on the front surface of the wafer. Once the coating mottle is formed as described above, for example, a focus in exposure processing is shifted, possibly failing to obtain a resist pattern with a desired dimension.
Further, in the aforesaid spin coating, a resist solution R badly breaks when the discharge of the resist solution R from a nozzle 101 to the wafer W is stopped, and a solution droplet R1 can drop as illustrated in FIG. 19 to FIG. 21. This solution droplet R1 possibly forms the aforesaid coating mottle.
Japanese Laid-open Patent Publication No. 2008-253986 discloses an example of the spin coating to prevent occurrence of the coating mottle due to the solution droplet R1. In this spin coating, the resist solution is supplied from the nozzle to the central position of the wafer rotated at a high speed, the rotation speed of the wafer is decreased into a low speed rotation with the supply of the resist solution from the nozzle being kept, the discharge position of the resist solution is moved to an eccentric position displaced from the central position of the wafer W, and then the discharge of the resist solution is stopped. Thereafter, the rotation speed of the wafer W is increased to dry the resist. The use of this method prevents rapid drying of the solution droplet R1 on the wafer W because of a low rotation speed of the wafer and makes the centrifugal force strongly act because the drop position of the solution droplet R1 is displaced from the center of the wafer W, whereby the solution droplet spreads while fitting into the surrounding resist to prevent formation of a coating mottle.